1. Field of Invention
The present application is directed to marine propulsion systems. More specifically, it is directed towards a hull mounted drive system that is both steerable and trimmable and which allows for the opening in the hull to be substantially sealed thereby allowing for greatly enhanced hydrodynamic efficiency and wake performance.
2. Description of Related Art
The general types of pleasure boat drives include inboard outboard (I/O) drives (or stern drives), outboard drives, inboard drives (including V drives) and pod drives. An outboard motor is a propulsion system for boats consisting of a self-contained unit that includes engine, gearbox and propeller or jet drive, designed to be affixed to the outside of the boat transom.
An I/O drive is a form of marine propulsion which combines inboard power with outboard drive. The engine typically sits just forward of the boat transom while the drive unit (outdrive) lies outside the boat hull. I/O drives are mounted on the rear most, vertical transom of the boat and offer advantages in the ability to trim, positively and negatively from neutral (water level), to adjust the running attitude of the boat. An I/O may include dual counter rotating propellers that are power efficient and deliver greater acceleration. However I/O drives nominally offer only +/−30 degrees of steering angle, and from their rear most mounting position on the back of the boat, I/O drives are at a disadvantage when it comes to steering and trimming leverage. This can result in excessive bow rise under acceleration and excessive roll when steering on plane. In addition, I/Os provide a significant prop strike risk to swimmers, surfers, tubers, etc. because the propeller of an I/O extends beyond the rear of the boat.
Inboard drive systems and V Drive systems typically have their propellers mounted under the boat and slightly forward of the rear transom, and offer superior leverage for steering and quicker time to plane with less bow rise compared with an I/O drive. However, traditional inboards offer no adjustable trim, nor do they traditionally offer dual counter rotating props. Therefore, it is recognized in the art that inboards are, typically, less efficient and can be 20% slower at top speed when compared with an I/O. Because they typically must rely on a rudder for steering, inboards also suffer from a lack of directional control in reverse. This can make docking difficult for inexperienced boaters. However, with the prop located a significant distance under the boat, the threat of a prop strike to a swimmer is greatly reduced.
Pod drives are relatively new power systems that eliminate the need for shafts, struts, and rudders. Instead of using traditional running gear to transfer the engine's power into thrust, a “pod” consists of the transmission, outdrive, and propeller(s) mounted through the bottom of the boat. The pod itself rotates to direct propeller thrust thereby eliminating the need for rudders. Pods generally have been developed for large motor yachts where they offer improved efficiency with the need for dual counter rotating props and greater low speed maneuverability because of a 360 degree of steering angle, but to date, pod drives do not offer trimming to adjust the running attitude of the boat. Instead, pods offer only trim tabs, which increase drag, to adjust the trim angle.
U.S. Pat. No. 7,485,018, issued to Wilson et al. on Feb. 3, 2009, discloses a marine drive assembly that includes upper and lower units in which the upper unit is pivotally attached within a cavity formed in the hull for adjusting the pitch of the drive assembly and further in which the lower unit is steerable. Among other things, Wilson teaches that his marine drive unit is disposed within a hull cavity that is exposed to the elements and expected to fill with water while the vessel is idle or underway. This also necessitates that the hydraulic motor for steering Wilson's drive unit is also exposed to water. Further, Wilson teaches the use of a push-pull rod for adjusting the drive unit's trim angle. It will be appreciated that Wilson's open hull cavity, which by design is expected to fill with water will adversely impact hydrodynamic efficiency and wake performance such that while Wilson's drive unit may be very serviceable for large slow vessels, Wilson's drive unit would not be well suited to high performance or sport boats for which hydrodynamic efficiency and wake performance are highly desirable traits. The present invention is intended to overcome these problems with hydrodynamic efficiency and wake performance in high performance and sport boats, to provide a more efficient and less space consuming method of trimming the drive unit, and also to prevent the hydraulic motor for the steering unit from being exposed to water.
Accordingly, it is an object of the present invention to provide a hull mounted, steerable marine drive system, similar to a pod drive, that also includes trim actuation. Another object of the present invention is to provide such a steerable and trimmable marine drive system while preserving the contour of the hull so as to provide greatly enhanced hydrodynamic efficiency and wake performance. Still another object of the present invention is to provide a marine drive system that is both steerable and trimmable that protects its hydraulic or electrical systems from being submerged in water. Still yet a further object of the present invention is to provide a marine drive system that is both steerable and trimmable that incorporates a foil that moves with the trimming of the drive unit which is adapted to provide enhanced lift both positively and negatively. These and other objects and advantages over the prior art will become apparent to those skilled in the art upon reading the detailed description together with the drawings.